FLA Formal Definition 9

[PUMPDESIGNER]

I am stuck on FLA (Full Load Amps) for motors.
Where does the formal definition of FLA come from?
I suspect NEMA may provide that, but I cannot afford to purchase MG1 unless I know that contains the definition.

I find many code uses for FLA, but in NEC and in the Freeby Condensed MG1 I find no definition.

When I boldly try to define it myself, It gets sticky with Service Factors, Code Letters, etc.

How does a motor manufacturer determine FLA?

PUMPDESIGNER

 

[ScottyUK]

Hi Colin,

I must disagree that an over-sized motor running open shaft or on a light load could draw a current greater than the motor's rated FLC. Granted, it will draw a fair magnetising current and the power factor will be poor, but the current will not approach FLC.

Are you perhaps looking at the motor's phasor diagram and meaning that the quadrature (reactive) component of current is greater than the in-phase component? This could well be true for the condition you describe.





-----------------------------------

Start each new day with a smile.

Get it over with.

 

[jbartos]

Comment on PUMPDESIGNER (Mechanical) Apr 2, 2004 marked ///\\jbartos,
Thank you for your comment, I see it this way.
SERVICE FACTOR may have a technical agreed upon definition, which if you know of a source for that definition I would appreciate knowing it.
///References:
1. NEMA MG-1
2. IEEE Std 100 "Dictionary"
Service Factor (general-purpose alternating-current motor) A multiplier that, when applied to the rated power, indicates a permissible power loading that may be carried under the conditions specified for the service factor.\\But SERVICE FACTOR generally means a fudge factor to account for field things that happen like voltage sag, a little unbalance, things like that which cannot be predicted.
///Yes and no. The service factor can be imagined as extra HPs built into the motor by the manufacturer, e.g. SF=1.15 would mean for the 500HP standard motor extra 75HPs. If the 575HP motor happened to be available, it would be equivalent to the 1.15 service factored motor. However, voltage sags more than 10%, voltage unbalance more than 2% or so are detrimental to standard motors as well as to service factored motors.\\For a pump manufacturer just to walk in and use that service factor without asking the customer means that there is no longer a service factor available.
///Absolutely correct. It is called fine tuning the motor-pump sets.\\ Those suckers can't seem to resist the tempation to grab something that provides a little cushion and makes life a little easier, pushing us onto the edge, and shortening the life of the motor.
///Absolutely correct. Money talks and keeps motor manufacturers in business.\\
Which then leads to the question, why have a stinkin service factor?
///Because not everyone is a sucker around. There are many many decent people around. For example, if there is a motor operated valve that has very hard unseating (a lot of sediment inside), a suitably rated motor with high SF helps.\\

 

[GOTWW]

Service factor is good for sizing your overloads. That's my take on it. I see the old 150HP pump motors running good looking clean. I see the new ones noisey and leaking brown substances. It is all about the money.

 

[PUMPDESIGNER]

jbartos,
I respect your opinions and thank you for the answers.
I get into a foul mood now and then, after I read my post I was a little embarassed.
I would have written those things differently on a better day, and you are correct in all that you say.

I know I have a legitimate gripe which I think you agree with:
If the motor manufacturer provides a service factor,
Users have a choice to use it constantly,
Or leave that service factor for abnormal conditions.
All is fine if they act wisely.

But over the years I have found that the service factor means nothing to many pump manufacturers except one thing, When they buy a 100 hp motor with a 1.15 service factor, they consider that they bought a 115 hp motor and they use it that way if they can, and if you do not like that you must be on guard to stop them. Drop your guard for even a moment, and you get the standard treatment, they take you right to the edge.

I suppose also that my viewpoint is that of a person not working in Alaska but in tropical climates, heat is our enemy and we get poor motor life if we are not careful.


PUMPDESIGNER

 

[jbartos]

Comment on the previous posting marked ///\\But over the years I have found that the service factor means nothing to many pump manufacturers except one thing, When they buy a 100 hp motor with a 1.15 service factor, they consider that they bought a 115 hp motor and they use it that way if they can, and if you do not like that you must be on guard to stop them. Drop your guard for even a moment, and you get the standard treatment, they take you right to the edge.
///It is sufficient to turn off valve a little bit to have the motor delivering 100HP instead of 115HP. In time, there may be some sediment instead of slightly closed valve so that the motor will be delivering 100HP shaft anyhow instead of 115HP.\\

 

[PUMPDESIGNER]

jbartos,

Yup, some processes result in lower flow rates over time,

But other processes result in higher flow rates over time due to age and wear on the hydraulic components. Irrigation systems are known for that behavior because each spray head has a nozzle, and each nozzle degrades over time becoming larger and larger, flow rates always increase on irrigation systems.

The second and ultimately the killer problem on irrigation is the fact that the pumps are often located in distant remote areas with lower voltage, smaller wire sizes, etc. So, if the pump guys take every bit of slack out of motor performance then the motors begin running hotter.

PUMPDESIGNER

 

[SteveKW]

But over the years I have found that the service factor means nothing to many pump manufacturers except one thing, When they buy a 100 hp motor with a 1.15 service factor, they consider that they bought a 115 hp motor and they use it that way if they can, and if you do not like that you must be on guard to stop them. Drop your guard for even a moment, and you get the standard treatment, they take you right to the edge.

So very true! Especially in the fractional HP pumps!

Dont forget to add impeller wear, making the pump pump too much!

 

[aolalde]

My comment about Service Factor (SF) in electric motors is to agree with the simple statement posted by GOTWW.

It is the “Overload allowed” if all other parameters are per specifications (Voltage, Frequency, Ambient, etc)

Some of the differences between Rated HP and Overload HP are the “Torque-Speed curve”, including staring and breakdown, Inrush current, Temperature rise, Efficiency and Power Factor.

The Rated HP must comply with all the standard specified parameters.
The overload has only to be carried without motor damage.

And without doubt is all about the money.

 

[buzzp]

I think the key here is the motor will run at SF. The length of time it will run at this level may or may not be reduced depending on the ambient temperature. The OL results in an increase in operating temperature. Any increase above the temp rating of the motor then we start seeing the life reduced. This is what OL protection is for-to prevent an over temperature situation.
I would discourage operating a motor above FLA for any length of time. If it needs to be done, it may be done with a probability of reduced life. If the motor has embedded RTD's or thermocouples then this would be the best way to determine if operation at the higher current will indeed reduce the life. Granted, temperature will change slow compared to the current so it won't act as fast as an overload but the temp can certainly be checked and compared with running amps and ambient temp.

 

[CB2]

I am late into this discussion and a little suprised there is no mention of temperature until April 13th posts. I think buzzp brings up a very important factor about motors and their ratings.

The definition of a motor is " an electro/mechanical device that is thermally rated".

 

[oxilume]

Pumpdesigner,

This article should clearly define FLA & FLC with respect to temperature.

http://www.ul.com/regulators/ode/1000.pdf

Todd

http://www.oxilume.com

 

[PUMPDESIGNER]

oxilume, I liked that article and saved it.
buzzp does bring in the correct balance to things.
If I had a motor working in Alaska running at outdoor temperature, I would not worry about that SF at all, (Probably get concerned with the grease or oil on bearings though).

But, our stuff is mainly South Florida, Caribbean, South and Central America, hot, hot, hot. We no likey to see SF used at all.

PUMPDESIGNER

 

[jbartos]

Comment on CB2 (Electrical) Apr 14, 2004 marked ///\\I am late into this discussion and a little suprised there is no mention of temperature until April 13th posts.
///Not quite. My previous posting point to the motor nameplate where the motor temperature parameters or limitations are addressed. Visit

http://www.ab.com/manuals/dr/Motors/Motors9_2.pdf

for: Figure 1 motor nameplate indicates the motor ambient temp 40C and "thermally protected"\\ I think buzzp brings up a very important factor about motors and their ratings.
The definition of a motor is " an electro/mechanical device that is thermally rated".